Composite materials are generally defined as materials containing a mixture of two or more constituents that are solid in the finished product, mutually insoluble, and differ in chemical nature. Such composite materials are highly attractive for many applications, typically because they possess unique characteristics relating to rigidity, toughness, strength, density, and particularly cost. Most composite materials are macroscopic combinations of an inorganic reinforcing material and an organic polymeric matrix material. The organic polymeric matrix material is generally either obtained from a thermoplastic or thermoset resin.
Composite materials are generally utilized in a prepreg form, i.e., a form in which the reinforcing material is combined with the resin before molding. That is, the inorganic reinforcing material and an amorphous, reactive, organic matrix material are combined prior to use as a composite. Typically, in a prepreg the organic matrix material is an amorphous thermoplastic material. The transformation of the amorphous thermoplastic material (i.e., a polymer that softens when heated and hardens when cooled) into a thermoset material (i.e., a polymer that becomes crosslinked when cured) can be initiated by an energy input into the system or by introduction of a catalyst or coreactant. An example of such a catalyst or coreactant is water.
The inorganic reinforcing material used in composites can be obtained from an organometallic compound when contacted with water. Many organometallic compounds, such as metal alkoxides, are known to undergo hydrolysis on contact with water to form the corresponding metal hydroxides. Metal hydroxides often undergo subsequent condensation reactions to form compounds having M-0-M bonds (M=metal). In this way, organometallic compounds can decompose to form an essentially inorganic reinforcing material.
In certain mixtures of organometallic compounds and organic polymers, the two components react to provide polymer-bound organometallic compositions. In such situations, there is little or no free organometallic compound to act as solvent for the organic polymer. Therefore, the viscosity of the derived composition would be very similar to that of the organic polymer itself. Such composite materials are of limited value because their viscosities cannot be readily controlled. Thus, they are not useful for a wide variety of for various applications.
In other mixtures of organometallic compounds and organic polymers, the organometallic compound is used simply as a filler or as a polymer swelling agent. In some situations, the organometallic compound acts as a plasticizer to increase the ductility, reduce the glass transition temperature, and reduce the brittleness of the polymer. In such applications, an organometallic compound is used in an amount of only up to about 25% by weight of the host polymer. These compositions are not suitable composite materials because they are generally not flowable and do not possess acceptable coating viscosities.
Some combinations of organic polymers and organometallic compounds also include a volatile organic solvent. Such mixtures are undesirable because of the need to evaporate the organic solvent from the composite material. The evaporation of an organic solvent in the preparation of a composite material is undesirable because of the potential environmental impact of the organic solvent, the associated increased energy requirement, and the limitation such a step places on the production rate of the composite material.
U.S. Pat. No. 4,879,065 discloses an organic solvent-free, high temperature mixture of an organic polymer with an organometallic compound. Solutions of organometallic compounds with organic polymers at temperatures in excess of 170.degree. C. are exemplified, but the existence and stability of these solutions at ambient temperature are not shown. Furthermore, because of the high processing temperatures required, the number of useful polymers is quite small, being limited to those that are heat stable.
Other organic solvent-free mixtures of an organic polymer with an organometallic compound incorporate reactive groups such as acrylates, isocyanates, and epoxides. In order to produce useful composite materials, such reactive groups are necessarily present in the organic species. Because of this, there is the potential that such reactive groups could contact the user of the derived product. Because of any perceived health hazards associated with such reactive groups, it is desirable to manufacture products that are essentially free of these highly reactive moieties.
Silicone polymers, such as polydialkylsiloxane polymers, have also been used with organometallic compounds. Such combinations are used in the preparation of silicone rubber having good high temperature properties. These silicone rubbers are not widely applicable composite materials, however, because they do not generally overcoat well, e.g., few paint formulations adhere well to them.
Therefore, a need exists for a resin composition that is stable under ambient conditions, is flowable, and is free of highly reactive, potentially harmful, moieties. Also, a need exists for a resin composition that cures with water under ambient conditions. Furthermore, a need exists for such a composition that is capable of possessing a wide variety of viscosities.